One fund got you here. Spending it takes a plan.

First, the credit they deserve.

I worked at Fidelity for five years, and I've watched target-date funds become the default in just about every company plan in America. There's a good reason for that. Most people don't want to pick funds, and HR can't give advice. So the plan hands you one fund with a year on it, and it does a better job than most people would do on their own. It buys, it rebalances, it gets a little more conservative every year, and you never have to think about it.

While you're working, that's exactly what you want. When the market drops, your next paycheck buys more at lower prices. The taxes are deferred. Nobody is taking anything out. The fund only has to do one thing: grow.

The problem is that retirement asks your money to do a completely different job.

Same fund, two different jobs.

Going from accumulation to distribution is the biggest change in your financial life, and most people make it holding the exact same fund they bought at 35.

Limitation one: every dollar comes out the same way.

A retirement plan that's built to last uses buckets. Near-term money, a few years of spending in cash and short-term bonds, so a bad market doesn't force you to sell stocks at a loss to pay the bills. Mid-term money in bonds and income to refill the first bucket. And long-term money in stocks, left alone for a decade or more.

The whole point is choice. When the market is up, you take your income from the growth bucket and sell high. When the market is down 20%, you leave the stocks alone and spend from the safe bucket. Recoveries don't run on a schedule, which is why that bucket holds years of spending, not months.

A single fund can't do that. Take $1,000 out of a fund that's 60% stocks and 40% bonds, and you've cashed out $600 of your stocks and $400 of your bonds. Every time, in every market.

You can't say "just sell the bonds this year, the stocks are down." And that is the entire reason you own bonds in retirement. The fund's rebalancing isn't wrong. It just isn't yours: it keeps the fund's mix, not your plan.

Limitation two: the same thing happens to your Roth conversion.

This is the one almost nobody sees, and it's the one I care about most.

Asset allocation is what you own. Asset location is which account owns it. And location is the piece almost everybody misses. My rule of thumb: your fastest-growing assets belong in the Roth, because qualified withdrawals of that growth are tax-free. Your slowest-growing assets, your bonds, belong in the pre-tax IRA, where slower growth means a smaller tax bill later. Accelerate the Roth. Decelerate the IRA.

Now try doing that from inside one fund. Convert $10,000 straight out of a 60/40 target-date fund and $6,000 of stocks and $4,000 of bonds move into your Roth together. The bonds come along because they're welded to the stocks inside one ticker.

Can you work around it? Yes. You can sell the fund inside the IRA, buy separate stock and bond funds, and convert only the stock piece, or swap it after the conversion and rebalance the IRA to keep your overall mix. But that's a set of trades someone has to plan and repeat every year. Possible isn't the same as simple, and in most of the households I meet, nobody is doing it.

Do it on autopilot year after year and you can end up with a Roth that's 40% bonds. In the plans I build, that's the wrong account for them. I say it this way: pay the tax on the seed, not the tree. I think of the Roth as the most valuable account you'll ever own. It shouldn't be holding your slowest money.

Limitation three: the "safe" half isn't as safe as you think.

The bonds inside a target-date fund are a bond fund. Most bond funds never mature. There is no date when you get a set amount back.

Bonds work like a see-saw. When interest rates go up, the price of the bonds you already own goes down, because a new bond pays more and nobody will pay full price for yours. If you own an individual bond, you can ride that out and hold it to maturity, and as long as the issuer pays, you get your $1,000 back. Inside a fund, you can't. And when other investors pull money out in a bad year, the fund has to raise cash to pay them. You're partly at the whimsy of everybody else in the fund.

With a portfolio of meaningful size, you can own a ladder instead: bonds that come due one year at a time, lined up with the income you'll actually need. To be fair, a ladder still has interest-rate risk if you sell early, and it takes building and tending. What it gives you is control. Nobody else's decision can force a sale of your bond.

Limitation four: the fund de-risks on its schedule, not yours.

A 2030 fund doesn't know you have a pension. It doesn't know your Social Security covers most of your basic bills, or that your Roth is money you don't plan to touch for twenty years. It just keeps sliding toward bonds as the year on the label gets closer, and keeps going after it passes.

For some people that's right. For a lot of the people I meet, it's backwards. The dollars that can afford to grow are being made more conservative, automatically, and nobody asked them.

Limitation five: five funds can still be one fund.

Here's a pattern I see all the time. A couple in their late fifties, good savers, two careers, more than a dozen accounts across half a dozen institutions. Every time they changed jobs, the new plan put them in a target-date fund. So they own four or five of them, from different companies, all dated within a few years of each other.

It feels like diversification, because it's Fidelity and Vanguard and T. Rowe Price. Usually it isn't. It's largely the same strategy bought several times. When you line them up, the mixes and results are usually close to one another. And every one of those accounts has its own beneficiary form, its own login and its own rules, which is a logistical mess for whoever has to settle things one day.

So what do you do instead?

None of this means target-date funds are bad. It means the job changed. Here's how I'd think about it:

1. Keep the same overall risk, in separable pieces. If you're comfortable at roughly 60/40, stay there. Just hold it as distinct stock and bond pieces you can sell one at a time.
2. Build the buckets before the last paycheck. Have the next several years of spending lined up in safe money, so a bad market in year one doesn't force your hand.
3. Point the Roth at growth. When you convert, move the growth piece first and leave the bonds in the IRA.
4. Simplify, carefully. Fewer accounts, fewer forms, one place to look. But some accounts are worth keeping: a current employer plan can give earlier access to money under the rule of 55, some plans have very low costs, and employer stock may qualify for special tax treatment that's lost if it's rolled over first. Look before you move anything.

Your fund's fees are probably not the problem. A lot of these funds are very inexpensive. The problem is that one blended fund can't be taken apart, and retirement is all about taking things apart: this account this year, that asset in a down market, this piece into the Roth.